The invention relates to a method and an apparatus for producing an elongated rod-like filler which consists of fibers, especially tabacco shreds. More particularly the present invention relates to a machine and method of making cigarettes or the like.
It is already known, particularly in the cigarette industry, to form a continuous stream, to advance the stream, to equalize the advancing stream by removing the surplus of fibers therefrom, and to densify and confine the equalized stream to form a wrapped filler (such as a cigarette rod which is severed to yield discrete cigarettes). It is further known to control the removal of surplus fibers in dependence on a signal wich is indicative of the mass flow of the equalized stream, preferably subsequent to wrapping of the stream.
Conventional apparatus for the practice of such method employ a conveyor on which the stream is formed and by means of which the stream is advanced, an equalizer which removes the surplus of fibers from the advancing stream at a trimming station, a device ffor densifying the equalized stream downstream of the equalizer and for confining the densified stream in a web, a device for monitoring the mass flow of the equalized stream, preferably downstream of the wrapping station, and a control arrangement which regulates the distance between the equalizer and the conveyor in response to signals from the monitoring device.
The term "densification", is intended to denote conversion of the equalized, but unwrapped, stream into a filler having the shape or cross section of the wrapped tobacco filler (or cigarette rod), from which discrete cigarettes are severed at regular intervals. Such conversion is performed by a so-called garniture in which the equalized stream is compressed during passage therethrough and which, consequently, acts as a densifying arrangement. However, in the event that the tobacco in the tobacco filler is already considerably compressed during advancement to the equalizing station and/or the garniture (for instance, by subjecting the tobacco stream on the air-permeable conveyor to the action of a pronounced subatmospheric pressure), it can happen than the cross section of the equalized tobacco stream is the same or even smaller than the cross section of the filler in the cigarette rod. Under such circumstances the expression "densification" is intended to denote conversion of the tobacco stream into a filler having the cross section of the wrapped cigarette rod. It is customary in the manufacture of cigarettes to control the formation of the tobacco filler which is subsequently densified, wrapped and subdivided into discrete cigarettes in such a manner that a constant quantity of tobacco (per unit length) is available in the wrapped cigarette rod and thus in each of the discrete cigarettes. For this purpose, one employs a monitoring device (e.g., a beta ray detector), which generates signals denoting the density of tobacco in the cigarette rod, and such signals are used to regulate the distance between the conveyor and the cutting plane of the equalizing or trimming devices which removes larger or smaller quantities of surplus tobacco from the filler. However, as a rule, the smoker cannot examine a cigarette as to its tobacco content. Consequently, the smoker evaluates a cigarette according to its hardness or rigidity, which depends on the filling force of tobacco. The hardness is determined by the resistance which the tobacco shreds in a cigarette offer to a force of such magnitude as to cause elastic deformation of the cigarette. The smoker can examine such hardness by pressing his or her fingers against the cigarette. In view of this, it can be advantageous to control the formation of a tobacco filler in a cigarette maker not for the purpose of maintaining the quantity of tobacco at a constant value, but rather to achieve constant hardness.
It is known to provide special devices for direct monitoring of the hardness of a wrapped cigarette rod. U.S. Pat. No. 3,411,513 discloses a nozzle which directs air against a cigarette rod, and means for ascertaining the extent of elastic deformation of the cigarette rod, the extent of such deformation denoting the hardness of the rod. Another monitoring device is disclosed in British Pat. No. 1,468,169 in which a contact roller is pressed against the surface of the tobacco rod with a predetermined force. Conclusions may be drawn from the elastic deformation and the corresponding change in position of the contact roller as to the hardness, and an equalizer can be controlled accordingly.
It has been established that the devices for direct monitoring of hardness and corresponding adjustments of the equalizer do not always perform to satisfaction.